Install aluminum window sill with expansion compensation

An aluminum sill reacts with strong expansion or contraction to temperature differences. Therefore, when installing, especially outdoors, great care has to be taken with regard to expansion tolerances and maximum length. In addition there is a sound insulation against driving rain.

Strain compensation is the focus

The material aluminum expands at a temperature difference of sixty degrees Celsius by 1.5 millimeters to one meter. Frost in winter and strong sunlight in summer produce this span easily and almost every year. This clearance must be taken into account during installation to prevent bulging, tearing or damage to the anchorages, façade and masonry. The main compensation is accomplished by an expansion spring with inserted stretch band.

When mounting an aluminum sill, lateral end pieces are inserted, which contain spring and band. Most components have an expansion tolerance of up to five millimeters. The maximum length of a continuous aluminum sill shall never exceed three meters. It is safer to split the sill in two-meter increments. Between the ends of a stretchable butt joint element is to be mounted.

Install aluminum windowsill extensively

  • Alu windowsill
  • Tails with stretch band
  • Possibly stretchable butt joints
  • Antidröhnband
  • Stainless screws
  • screw covers
  • Dowels (possibly expansion dowels)
  • sealing tape
  • Silicone or polyurethane foam
  • Mounting foam or assembly adhesive
  • screwdriver
  • caulking gun
  • drilling machine
  • drill

1. Place fasteners

Drill the mounting holes in the lower window frame and possibly holes for the butt joints to be placed.

2. Attach end pieces

Attach the side end pieces to the aluminum windowsill with the inserted stretch tape.

3. Check the expansion tolerance

Hold the aluminum window sill in the niche and check the joint widths sideways. Make sure that the end pieces are correctly attached and fully inserted.

4. Check drip edge clearance

Measure the overhang, which must not be less than four centimeters. If the projection of the windowsill is not sufficient, you must obtain a wider copy.

5. Seal and insulation

Attach the sealing tape or profile to the lower window frame, glue the anti-noise foil to the underside of the windowsill and screw the placed bank.

6. Grouting

If, in addition to the end pieces joints arise or remain, fill them with silicone or polyurethane.

Tips & Tricks

The sealing tape that Se use should be a vapor-permeable tape that avoids condensation despite driving rain.

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